1. Field of the Invention
The present invention relates to a gas sensor.
2. Description of the Related Art
In recent years, a fuel cell which attracts attention as a power source of a fuel cell vehicle, etc., exhausts hydrogen (a detected gas) unconsumed in power generation from an anode. This hydrogen is diluted with a cathode off gas (a dilution gas) from a cathode of the fuel cell, and is exhausted to an exterior (an outside) of the vehicle.
A hydrogen concentration of the gas (a diluted gas) exhausted to the external of the vehicle in the above described manner is detected by a catalytic combustion type hydrogen sensor (a gas sensor) (see JP 2004-251862 A). Also, since a detection element to catalytically combust the hydrogen deteriorates with the use of the hydrogen sensor, the hydrogen sensor is provided with a normal detection element pair and a reference detection element pair.
In particular, the normal detection element pair is provides with a first detection element whose temperature is raised and whose resistor value is changed by contact with the hydrogen, and a first compensation element (a temperature-compensated element) which is inactive to the hydrogen. The reference detection element pair is provided with a second detection element whose temperature is raised and whose resistor value is changed by contact with the hydrogen and a second compensation element which is inactive to the hydrogen. Also, (1) at the time of normal operation, the reference detection element pair is not energized, but the normal detection element pair is energized and activated so as to detect a hydrogen concentration, and (2) at the time when deterioration of the normal detection element pair is determined, and the reference detection element pair is energized and activated, an output of the normal detection element pair is compared to an output of the reference detection element pair so as to determine whether the normal detection element pair deteriorates or not.
However, since the hydrogen sensor disclosed in JP 2004-251862 A is provided with a first element housing which houses the normal detection element pair and a second element housing which houses the reference detection element pair, the hydrogen sensor can not be minimized. Also, when a plurality of element housings are provided, a heater for heating a detection chamber in the element housing and a temperature sensor for detecting a temperature in the detection chamber are required for every element housing. As a result, the number of parts is increased, and the cost for manufacturing the hydrogen sensor is increased.
For this reason, as disclosed in JP 2004-251862 A, the normal detection element pair and the reference detection element pair can be placed in one element housing. However, a thermal interference may occur between the normal detection element pair and the reference detection element pair. As a result, a detection accuracy of the hydrogen concentration may be lowered.
Therefore, an object of the present invention is to provide a simple gas sensor for detecting a concentration of a detected gas with high accuracy.